Rotor heat shields serve to provide a platform in the gas flow path and on the radially inner side of a vane. Typically they form together with a honeycomb seal a labyrinth seal on its radially inner side. The rotor heat shield combined with the honeycomb seal reduces flow losses between stator and rotor and thus improves gas turbine efficiency.
In the region of a gas entry and exit to and from a rotating blade, rotor heat shields typically have a complex shape including several bends. FIG. 1 shows a section of a gas turbine of the prior art including a rotor 1 having a rotor axis 1a, rotating blades 2 and a vane 3 mounted on the rotor. Bold arrows indicated a gas flow path, and a rotor heat shield 4 is arranged opposite the vane 3 in the gas flow path. The heat shield 4 is formed having bends, in particular in the regions A and B, which relate to the regions of gas entry and exit to and from a rotating blade, respectively. A cooling air supply cavity 5 is provided on the rotor side of the rotor heat shield 4, and cooling air is allowed to pass along the rotor side of the heat shield as indicated by the dashed arrows. The rotor heat shields 4 are arranged adjacent to one another in the circumferential direction of the rotor (in FIG. 1 out of the page) and are joined to the rotating blades 2 in the axial direction. A seal or seal assembly 6, 7 is arranged on the rotor heat shields 4. The seal assembly allows sealing of the space between adjacent rotor heat shields as well as sealing of the space between rotor heat shields and rotating blades. As such it serves to prevent cooling air from cooling spaces on the rotor side of the rotor heat shield from leaking into the gas flow path. Thus, the cooling air mass is maintained, and engine performance is assured.
Typically, the seal assembly comprises individual seal parts 6 and 7, each placed in a groove of the rotor heat shield and having several bends according to the bends of the rotor shield 4 and the groove therein. The individual seal parts 6 and 7 are configured to overlap one another at their end portions allowing for air tightness. They further overlap with end portions of seals 8a and 8b arranged at the rotating blades 2. Both seal parts 6 and 7 and their respective groove extend in the turbine axial direction, along a first bend to the turbine radial direction, along a second bend and again in the turbine axial direction. There, at the location where the rotor heat shield meets the rotating blade, the seal parts 6 and 7 each have an additional section extending in the turbine circumferential direction (extending out of the page of the figure) sealing the space between heat shield and blade.
The air tightness of the seal assembly however, can be compromised because the sealing surfaces cannot simultaneously match all the bent surfaces of the rotor heat shield 4 within given tolerances.
In addition, the cast parts can deviate in their dimensions and/or can get displaced relative to parts of adjacent rotor heat shields during turbine operation. This can aggravate the air tightness of the air cavity and result in a risk of increased loss of cooling air and thus reduction of the turbine performance. Problems can further arise during the mounting process. Frequently, the seal must be deformed in order to enable mounting on the rotor. This deformation can lead to radial gaps in critical areas resulting in additional air leaks.